Process for the manufacture of high volatile carbon black



May 20, 1947. R. l. BRAY ETAL PROCESS FOR THE MANUFACTURE OF HIGH VOLA'IILE CARBON BLACK Filed Dec. 18, 1941 2 Sheets- Sheet l i M QZWM May 20, 1947. R! l. BRAY ETAL 2,420,810

PROCESS FOR THE MANUFACTURE OF HIGH VOLATILE CARBON BLACK 2 Sheets-Sheet 2 Filed Dec. 1 8,, 1941 Patented Merit}, 1947 UNITED STATES raoonssv 1301i was EPAT crimson may:

Lame cannon annex Richard LBx-ayi Gloucester, Jacob Gabry, Santos,-

. and'Charles'B. Wendell, Jr., Needham, Mass assignors to Godfrey. L. Cabot, Inc. Boston Mass, in corporation of Massachusetts Application December-'18, i941, Serial No. 423,512

it in accordance with the use for which it is-intended. The invention includes within its scope a new and improved carbon black of substantial volatile content, in some forms a higher volatile content that has ever before been' known, and also the novel process for producing such carbon black. i

The United States Bureau of Mines, Bulletin No. l'92,is authority for the statement that the volatile content of commercial carbon black runs from 5.33% to 14.44%, althoughin practicea somewhat wider range is encountered.

An analysis of the volatile contentof a typical commercial carbon black sample having a volatile content of 4.49% is published in Industrial and Engineering Chemistry for September 1928 in an articleentitled Carbon Black-+21 Study of its Volatile Constituents as follows: Percent weight Carbon dimlide 1.1'78 Illuminants 0.030 Oxyaen 0.071 Carbonm 2.805, Hydrogen 0.084 Ethane 0.002 Methane--- 0048 Nitr g T 0.205

In the present specification and claims the term volatile content is used, as it is commonly in the carbon black industry, to mean the per centag'e oi the constituents above listed which the carbon black contains. a

Heretofore carbon black having a volatile content as high as has been produced by heating to moderate temperatures while admitting a controlled amount of air thereto, as suggested in Reissue Letters Patent No. 19,664, Damon. .In carrying out that process, however, there generally occurs a serious loss oi! carbon black by combustion, thatis to say, a substantial proper tion of the treated material is destroyed in increasing the volatile content .of the remainder. It is commercial practiceto calculatethe surface area of carbon black byimeasuring its ad- 2 l V sorption of liquid nitrogen at minus 196 C The surface area of certain standard grades of carbon black hasbeen determinedasapproximate- 1y 110 sq. meters per gram of carbon black. When such carbon blacks areheated, as in the process of the Damon patent aboveidentifled, their surface area is greatly increased, to asmuch as 1000 sq. meters per gram ior example. with this increase in surface area occursa concomitant and objectionable falling of! in flow and an objectionable tendency toward thixotropy when the treatedcarbon black is mixed with liquid.

'i -Our invention is based onithe discoverythat the volatile content of carbon blaclr' may be increased by treatment with 'nitric, acid orf certain ,other i nitric oxidizing ;agents. without substan 'itiabcombustion lossand without other incidenital changes, in phflical properties which have j heretofore characterized carbon black having jsubstantialjmiatu content. An important ob- .ject of our invention is to producecarbon black having a substantialvolatile content, '1. e. more than 12%, and at the same time low or moderate "surface area, for enample, not over about 400 square meters per .gram, little or no tendency to thixotr'opy 'andiong flow characteristics. It has mot beenipossible to obtain such carbon black by a y processes heretofore known and used. By

w flong flow" characteristics we mean the char i acteristics so d ated in the Bureau of Mines BulletinflNo; 192,;jhich terminology is consistent "the volatile content or. carbon black may be increasedtdas much as 30-60% as compared with ore" considered the ,maximiiiri i 1 1 10-20% hereto! practical.

40 flirbon black treated according to our mention tends to become increasingly hydrolbhilic, whereas all ordinary carbon black is organo'philicl The hydrophilic tendency of the black treated according to our invention reaches the maximum inthose blacks 0! about 50% volatile content and over, and these form stablesusnsions in aqueous media without the necessity i f fusing a dispersing agent. j v V 2 Although we have not as yet explored all the possible uses of carbon black produced by the iwith accepted "ufl ge of the carbon black indus- Y further object of our invention is to provide E}; practicable and inexpensive process by which process of the invention, such experiments as have been performed indicate that itis useful in explosive compounds and that superior inks may be obtained by its use, since thixotropy is lessened, the body-is improved, and in long inks an astonishing increase inflow is noted. Moreover, these desirable results are secured in accordance with our improved process without loss of color intensity. Heretofore, it has been necessary to sacrifice color to improve flow, but the product of our invention has both intense color and long flow.

Although an improved product can be obtained by adding liquid nitric acid to carbon black and then washing the mass to remove excess acid, such a procedure is accompanied by the formation of indispersible agglomerates, and the product is therefore not suitable for uses where dispersion is required. However, superlative results may be obtained by passing a heated mixture of nitric acid vapor and air through a dry,

heated mass of carbon black, and later flushing the mass with hot air to remove excess fumes of the acid.

In carrying out the process of our invention any suitable or conventional apparatus may-be employed. One satisfactory type is illustrated in the accompanying drawings in which,

Fig. 1 is a diagrammatic view of the apparatus in side elevation, and

Fig. 2 is a curve showing the increase of volatile content of the carbon black during treatment.

The apparatus includes a heavy glass cylinder l which has hollow shafts and ii at either end. The shafts turn in bearings provided by a pair of standards 9, which support the cylinder in horizontal position. In the end walls of the cylindrical container I0 is a pair of opposed doors or plates I 2 by means of which carbon black can be loaded into the container and removed from it. A strip of Nichrome resistance wire is wound around the surface of the container l0 and secured at its ends to metal rings II which are rigidly secured to the hollow shafts l4 and IS. A brush I8 is mounted to bear upon each. of the rings l1, and current from a suitable source is applied to the brushes so that the container 10 and its contents can be heated. Preferably, and as herein shown,-the rotary container I0 is provided with one or more internal fins or vanes l3 by which the carbon black to be treated is lifted and spilled back and forth as the container is rotated, thus insuring complete contact of the carbon black particles with the vapor passing through the container. The container [0 may be rotated by any convenient means and we have indicated at 8 a sprocket fast on the shaft i which may be driven by a chain coupled to a slow speed motor or speed reducing mechanism.

At the left end of the container I0 is an inlet pipe I8 connected to the hollow shaft 14 by a swivel joint and to a pipe 20 controlled by a valve 22 and leading to the top of a flask 24 set in an open tank 26 which ispartially filled with water. Nitric acid, 70% concentration is contained in the flask 24. The tank 26 is adapted to be heated by a burner 28 located beneath it. A pipe 30 controlled by a valve 32 leads through the wall of the tank 26 and into the flask 24. The pipe 30 is connected to a vertical pipe 34 leading from a supply of compressed air and controlled by a valve 36. The pipe 34 is extended through the section 38, controlled by a valve 40,

4 to make connection with the inlet pipe H3 at a point just outside its swivel connection with the rotary container.

At the other end of the container 10 is an outlet pipe 46 which is connected to the shaft l5 by a swivel joint and runs into a condenser 48. A plug 39 of glass wool is inserted in the outlet shaft 15 to prevent carbon black from escaping from the container l0. A suction line 50 is connected to the top of the condenser, and a valve controlled outlet 52 leads from the bottom of the condenser. The condenser 48 may be cooled, if desired, by any suitable means (not shown).

In practicing the process'of our invention we heat the tank 26 until the water boils and simultaneously heat the container in to approximately 300 F. The valves 40 and 52 are closed, and the valves 22, 32, and 36 are opened. Air from the pipe 30 bubbles through the nitric acid which gives off copious fumes. The heated mixture of air and acidfumes are passed through the container Hi. The mixture may, if desired, be drawn through the container by means of suction through the pipe 50. At first the reaction of the carbon black in the heated container 10 and the acid fumes evolves heat, so that it is desirable to switch off the supply of current to the resistance wire l6, temporarily.

.Asfshown in Fig. 2, the increase in volatile content is at first very rapid, then the rate of increase slows down, and the addition of volatile content increases steadily but slowly for about twelve hours. Large quantities of N02 are evolved until the reaction stops, when the volatile content exceeds 60%. Thereafter the production of N02 practically stops and nitric acid distills in the condenser. By connecting the pipe 50 to washing towers it is possible to recover N02 and NO.

It will be evident that the apparatus described permits controls of different kinds over the process; the temperatures of the carbon black being treated and of the acid, the rate of flow of air into the flask 24, and the concentration of the acid, may all be varied to affect the result.

The carbon black should, of course, be maintained at a temperature higher than the boiling point of the nitric acid to prevent wetting and consequent agglomeration of the carbon black. We have found that the optimum results are obtained when .the carbon black is maintained at 300 F. Experiments carried out at more elevated temperatures seem to show that the surface area is undesirably increased and the yield is relatively poor. Incidentally, nitrogen may be substituted for air as the diluent for the acid fumes without affecting the result.

When the reaction has been accomplished, the valves 22 and 32 are closed and the valve 40 is opened. The carbon black in the container is flushed with air until the acid fumes have been entirely driven off. The temperature of the carbon black in the container may advantageously be raised to 400 F. near the end of the flushing period.

The treated black may be removed by swinging down the plates I2 and I4 and pushing the black from the container Hi. The treated carbon black will be found to have a volatile content according to the conditions of temperature, acid concentration, and rate of air supply at which the apparatus was operated. With air saturated at 212 F. with 70% commercial nitric acid, and with the carbon black at 300 F., and employing such a flow of air that the contact time of the gaseous mixture'in the container is about 50 seconds, the surface area oifithe carbon black will not have increased substantially; the volatile content may reach60 and the losses of carbon black during treatmentare, not sum cient to render the process unecononiicali It appears that'the carbon black product of our process is unique in that certain of the valuable properties are enhanced toa considerable degree over those commonly encountered in ear bon blacks treated with air at elevated temperatures. We cannot describe the nature ot the volatile content thus formed onthe surfaceof processror tile predicti ns: black having af'volatile contentjimexcess of 12%, a moderate "surfaceiarea andlong flow characteristics, whiehcomprisesjthe step of passing nitric acidvaponthrough a' mass of carbon black in a dry state removing free :nitric acid vapor from the treated black;

2; Ayproce'ssfor the:productionofcarbon black having a volatile content in excess of 12%, a

the black except to suggest that it consists in part of complex, little known oxidesof carbon.

However, the difference is well brought out by the fact that carbon black prodced by our process and having over 13% volatile content ishydrophilic. When untreated carbon black, or carbon black treated by other processes to increas'e its volatile content, is shaken with water and then,

with benzene, the carbon black will transfer at once to the benzene.- Now we have discovered that when carbon black treated by our process to I increase the volatile content to roughly 13% is shaken first with water and then with benzene,

moderate surface area and long flow characteristics, whichcomprises the steps of passing a hot mixture of nitricacid vapor and air through *vamass of carbon black heated at leastto 200 F.

and not over 400" F., and then removing free nitric acid vapor from thetreated mass.

'3. A process for the production of carbon black having a volatile content in excess of 12%, a moderate surface. area and longflow characteristics, which includes the step of passing nitric acid through a mass of agitated carbon black at a. temperature not exceeding, 400 F. i

4. A process for the production of carbon black having a volatile content in excess of 12%, a

rnoderate surface area and long flow character istics,-which includes the'step of passing heated dilute'vapor of nitric acid through a mass of the carbon black willxnottransfertothe benzene, but remainsinthe water. Accordingly,- one distinguishin'g characteristic of our novel product is its hydrophilicnature.

An analysis of volatile constituentsdriven'oifv a sample or Mogulf' carbon black havinga volatile contentof 60% and'produced in 'accordance carbon black in a dry state at a temperature not exceeding 400? F. for a period of at least five hours. i

" '5. A process for the production of carbon black having a volatile content in excess of 12%, a

a moderate surface area and long flow character- ,lstics, which comprises passing a mixture of with the invention Lherein disclosed, shows that the gaseous constituents were distributed as IQl- Q lows: 2 1 a by our process to a volatile content or over150% immediately disperses in water toforin ajstable colloidal suspension. The dispersionis automatic i and requires no shaking, or other treatment to start it. A dispersion-of ordinary carbon black can be formed only by "grinding'or by using a dispersing agent, and the result is not stable but Q 1 7 Another unique result of the practice "orourf invention is the fact that carbon black treated passes from the waterjinto benzene very readily, n In viewof these facts it is evident that we have invented a high volatile carbon black or different nature from that known -before,but can only describe it by the terms or its manufacture.

' It will fbeevidentl to I those skilled in the art that the'hot nitricxacid vapors are subject to a degree of decomposition and that the oxides of nitrogen so formed, inaddition to the acid vapors, are active in combining with the carbon black to increase its volatile content. Experiments have shown that by substitutingheated oxides of nitrogen for the nitric acid a carbon black having a high volatile content may be secured, although it is not now convenient to secure NO: in commercial quantities. However, the

scope of our invention definitely includes the use of gaseous oxides of nitrogen with or without suitable diluent gases, such as nitrogen, fiue gases,

etc.

Having thus described and illustrated the process of our invention and the novel and useful product thereof, what we claim as'new and desire to secure by Letters Patent of the United States is:

nitric acid vapor and a diluent heated to about 212*", through a mass of carbonblack in a dry therein, the, carbon blackl being initially heated by the resulting reaction and then tending to cool, and after this initial stage continuing the i process with the addition of external heat to the carbon black under treatment.

7 A process for the production of carbon black having a volatile content in excess of 12%, a moderate'surface area and long flow characteristics, which comprises placing impingement carbon black in a dry'state in contact with hot vaporsof nitric acid and oxides of nitrogen, and then flushing the treated carbon black to remove free-vapors.

8. A process for the production of carbon black having a volatile content in excess of 12%; a moderate-surface area and long flow character istics, which comprises placing carbon black in a dry state in contact with gaseous oxides of nitrogen, and then flushing the carbon black which has been so treated to remove excess oxides of nitrogen. FE

9. A process for the production of carbon black having a volatile content in excess of 20% and a moderate surface area, whichtcomprises passing nitric acid vapor through a mass of carbon black maintained in a dry state above the boiling point of nitric acid. 10; A process for the production of carbon black having a volatile content in excess M207, and a moderate surface area, which comprises mixing hot nitric acid vapor with a gaseousdiluent and passing the mlx'turethrough an agitated mass 9 of heated carbon blackln a'dry state. $9,? g??? 111133581924 figgg gg g 1,632,845 'Oberle June 21, 1927 CHARLES, B J 2,005,022 Damon June 18, 1935 1 ELL 5 1,191,333 Aylsworth July 1a, 1916 REFERENCES CITED I 2,312,707 m z, .1943 The following references are of record in the OTHER. REFERENCES file of this patent: 10 b B k i UNITED STATES PATENTS Chg: 5128x1226 repr at from Ind. a11 Eng. Number N me, Date "Acetylene Carbon Black, article in, 'Can.

8 1,989,107 Morre1l- Jan. 29, 1935 Chem. and Metallurgy, vol, 17, pages 93595. 

